I've looked around and found a few things...
Neem is available as a shampoo or spray to kill adult fleas. Citronella and other insecticidal herbs such as natural pyrethrum, mullein (Rotenone,) or Canadian fleabane can be prepared as a dip or as powdered herbs to use on the pet as well.
Using diatomaceous earth in the environment (around the house, both inside and out,) borate products inside on carpeted areas, and microscopic beneficial nematodes in the yard (the ONLY thing that also kills the resistant flea coccoon) complete the natural treatment for fleas. While feeding small amounts of fresh garlic and brewer's yeast to the pet have not been shown in controlled studies to be effective, many pet owners swear by their use and continue to add them to the diet to aid in parasite control.
Gentle Touch Flea Drops For Cats, Farnam
All-natural weapon in the battle against fleas. The first and only spot-on that controls fleas on pets with natural ingredients. An effective alternative to chemical flea control products. The two active ingredients (sodium laurel sulfate and citric acid) in Gentle Touch combine to dissolve the fleas' protective outer shell and interfere with their breathing. Kills fleas for up to 4 weeks.
To aid flea-scratching pets, the Tilfords recommend this herbal flea rinse recipe:
1 part feverfew flowers
1 part mullein flowers
1 part yarrow flowers, leaves and stems
1 part grounded celery seeds
3 parts calendula flowers
Place these fresh ingredients in a saucepan containing 2 cups of boiling water. Turn off the heat and allow it to cool. For added flea-flee strength, add 6 to 10 drops of bitter orange essential oil for every 8 ounces of rinse.
This link has a lot of info too:http://www.holisticat.com/fleas.html
Hope some of this info helps you out...